What kind of sewing machine should I get to last me for basically the rest of my life?

With sewing machines you basically get what you pay for.  If you want a machine that will last don't buy a cheap Walmart/Target sewing machine.  In my opinion the BEST sewing machines are the older Singers that were all metal.  I had one that was over 40 years old and ran like a charm.  That machine would sew through anything!  Alas, a ill-guided child cut the unplugged cord in half one day.  I had it spliced back together but it shorted out.  At this time I have a 1920's portable Singer that I wouldn't trade for anything.  It's my baby. Anywho.....

You didn't say what kind of machine you were looking for.  Husqvarna is an excellent brand and offers many different types of sewing machines from basic machines to full blown embroidery machines with all the bells and whistles. http://http://www.husqvarnaviking.com/us/17277.htm

Bernina and Pfaff...They are all great brands.  Chances are it will come down to a price point.  What are you willing to pay for that machine that will give you years of use and enjoyment?
  Your local sewing center is your best bet to look at new machines and even try them out.  Also, if it comes to your area, the Original Sewing and Quilting Expo is a great place to see the latest machines and accessories for sewing.  http://www.sewingexpo.com/

With all that being said, avoid buying a USED machine from Ebay unless they specifically state that the machine works and offer a money back guarantee.  A lot of sellers on Ebay don't know a sewing machine from a onion chopper.  They plug them in, see that they run and post them as working without knowing if they sew correctly.

Finally, whatever machine you decide on take care to make sure it gets proper yearly maintenance from a qualified professional.  This will keep your machine in good working condition for many years to come.
 

I love PFAFF machines, I used one for the first time this weekend and it was fantastic. I really like Brother as well. Honestly if you want one that will last forever, get one that has been around forever Bernina make fantastic machines, My grandma has one from when she was young and it still works as good today as it did the day she got it.

Call a quilting Store in your area...the ONe I went to..swears by the
Pfaff Machines...I know Viking machines are good too..SUSIE

Here are some best ones in these categories! Didn't quite know what type you were searching for so I would suggest reading reviews on them before deciding on any of them. They are good for what they can do but you might want something with more features on them. ; )
Singer:
Combining advanced technology with an array of user-friendly features, this electronic sewing machine will be appreciated by experienced and novice sewers alike. The unit's exclusive Drop & Sew bobbin system places the bobbin thread exactly where it's needed, while its built-in needle threader makes quick work of threading the eye of the needle--no more wetting the tip and squinting through multiple attempts. d edited for enhanced stitch variation.